1. Field Of The Invention
The present invention relates to a coordinate input apparatus, and more particularly to a coordinate input apparatus which detects the position of pressure applied to an input surface.
2. Description Of The Related Art:
Image input apparatuses such as those in which, for example, a user traces on or applies pressure to a board which is used as an input surface using a pen or the like, and the marks made by the pen are then portrayed as an image on monitor apparatus or are stored in memory as image data, are well known.
This kind of image input apparatus is used in, for example, games and graphics. Here, in order to detect the input position which is being drawn on the input surface, a coordinate input apparatus which detects the pressure position, i.e. the input position, as X-Y coordinate data on the input surface is used.
A coordinate input apparatus has a structure as shown, for example, in FIG. 1. In FIG. 1, numerals 1 and 2 indicate input detection members, with the first input detection member 1 having a rectangular resistance surface RY. Electrodes 1a and 1b are then formed at each of the long sides of this resistance surface RY. The second input detection member 2 has a rectangular resistance surface RX having electrodes 2a and 2b formed at each of the short sides thereof.
Sheet-shaped insulation sheets formed using, for example, PET, are used as the substrates for the input detection members 1 and 2. Rectangular resistance surfaces RX and RY are then formed on the surface of these substrates using, for example, a carbon printing process.
A voltage of, for example, 5 V is applied to the electrode 1a via the switch 3 and the electrode 1b is connected to earth via an external variable resistor Rg and a switch 4.
A voltage of, for example, 5 V is applied to the electrode 2a via a switch 5 and the electrode 2b is connected to earth via a switch 6.
Also, the electrode 1a is connected to a terminal Tx of a switch 7 and the electrode 2a is connected to a terminal Ty of the switch 7.
Numeral 8 indicates an A/D converter for converting the voltage supplied from the switch 7 into digital data, numeral 9 indicates an image memory section for storing digital data outputted from the A/D converter 8 as inputted coordinate values and numeral 10 indicates a controller for controlling the operation of the image memory section 9 and the switching of the switches 3 to 7.
In this coordinate input apparatus, the input detection members 1 and 2 are overlaid via the spacers SP, so as their resistance surfaces do not come into contact with each other, as shown in FIG. 2. Then, the surface sheet 11 becomes the input surface. An image input apparatus 12 such as that shown in FIG. 3, for example, can then be made using this kind of coordinate input apparatus. The area 13 of the image input apparatus 12 indicated by slanting lines is the input surface, which is made up of the input detection members 1 and 2. If a trace is made with a pen P on this input surface 13, the position coordinates for each of the pressurized points are detected by the coordinate input apparatus in FIG. 1 and stored in the image memory section 9. Although a detailed explanation is omitted here, by sending the data stored in the image memory section 9 to the monitor 14 as an image signal, images traced with a pen P on the input surface 13 can be outputted as images on the monitor.
The coordinate input apparatus is such that if pressure is applied to a point with a pen P in the manner shown in FIG. 2, resistance surface RY and resistance surface RX make contact only at the portion to which pressure has been applied. The values for the X and Y coordinates on the input surface are then obtained by detecting the resistance at this time. The operation for detecting these X and Y coordinates is described below.
In FIG. 1, the controller 10 outputs a switching control signal Ssw of, for example, 1 kHz pulses, to the semiconductor switches 3 to 7. Each switch then switches between the state shown by the solid line and the state shown by the dotted line in the diagram by way of the switching control signal Ssw, in 1 kHz cycles.
When each of the switches 3 to 7 is in the state shown by the solid lines, the X-coordinate for the input point is being detected, i.e. a voltage of 5 V is applied to the electrode 2a of the input detection member 2 and the electrode 2b is connected to earth. It follows that the values for the voltage will differ along the resistance surface RX in the X-axis direction. In an example under ideal conditions, the voltage would be 5 V at the portion connected to electrode 2a, 0 V at the portion connected to electrode 2b and 2.5 V at a position midway along the direction of the X-axis.
On the other hand, regarding the input detection member 1 at this time, the electrode 1a acts as the detection terminal for the X-coordinate, i.e. the output voltage from the electrode 1a is sent to the A/D converter 8 via terminal Tx of switch 7.
If a given point is then compressed, the resistance surface RX and the resistance surface RY come into contact at the compressed point. The voltage between the electrode 1a and the point on the resistance surface RX which has been compressed is then taken as the X-coordinate voltage. This voltage is then converted into digital data by the A/D converter 8 before being input to the image memory section 9 as the X-coordinate.
Alternatively, when each of the switches 3 to 7 is in the state shown by the dotted lines, the Y-coordinates for the input point are detected, i.e. a voltage of 5 V is applied to the electrode 1a of the input detection member 1 and the electrode 1b is connected to earth via the external resistor Rg. It follows that the values for the voltage will differ along the resistance surface RY in the Y-axis direction.
Regarding the input detection member 2, the electrode 2a acts as the Y-coordinate detection terminal, i.e. the output voltage for the electrode 2a is sent to the A/D converter 8 via a terminal Ty of the switch 7.
In this state, the voltage across the resistance surface RY to the point at which the input surface is depressed, i.e. the voltage value as a Y-coordinate, is obtained from the electrode 2a. This voltage is then converted to digital data by the A/D converter 8 before being inputted to the image memory section 9 as the Y-coordinate.
By constructing the coordinate input apparatus in this way, it is possible to input items such as images.
A further example of a construction for a coordinate input apparatus is shown in FIG. 4. Portions which are the same as portions in FIG. 1 will be given the same numerals and a detailed description thereof will be omitted.
Here, the input detection members are indicated by numerals 15 and 16. The input detection member 15 is rectangular, with a resistor RY formed along its short end with respect to the input surface so as to follow the direction of the Y-axis. Electrodes 15a and 15b are provided at both ends of this resistor. Conductive wires 15c protrude from the resistor RY so as to run parallel to the X-direction. These conductive wires 15c are formed at intervals of pixel units in the Y-axis direction.
The input detection member 16 has a resistor RX formed therealong in the direction of the long side of the rectangular input surface, i.e. the X axis direction. Electrodes 16a and 16b are then set up at each end of this resistor RX. Conductive wires 16c running parallel to the Y-axis direction then protrude from the resistor RX. These conductive wires 16c are spaced at intervals of pixel units in the X-axis direction.
In this case, the coordinate detection method is almost the same as that for the example in FIG. 1. If pressure is applied to a point on the input surface, one or more of the conductive wires 15c and one or more of the conductive wires 16c will come into contact with each other. It follows that when each of the switches 3 to 7 is in the state shown by the solid lines, the voltage at the resistor RX corresponding to the X-axis coordinate is taken from the electrode 15a. Also, when each of the switches 3 to 7 are in the states shown by the dotted lines, the voltage at the resistor RY corresponding to the Y-axis coordinate is taken from the electrode 16a. These voltages are then converted into digital data by the A/D converter 8 before being put into the image memory section 9 as the coordinate data.
With this kind of coordinate input apparatus, the input surface which acts as the X and Y coordinate detection region corresponding to the monitor screen for the image input apparatus of the kind, for example, shown in FIG. 3, is usually rectangular. That is to say, the lengths of the X-axis and Y-axis are different.
Since the lengths of the X and Y axes which are taken as the coordinate axes are different, the number of pixels allotted to the X and Y directions in the memory for storing the detected coordinate data is different.
Also, the same voltage is applied to the resistors RX and RY for the X-axis and the Y-axis. Voltages are obtained which correspond to X-axis and Y-axis coordinates and these are then converted to digital data using the same A/D converter 8. This, however, means that the coordinate data obtained from the A/D converter 8 and the pixel memory allotted to the coordinate positions in the image memory section 9 become incompatible.
For example, the following points should be considered: the ratio between the size of the coordinates for the X-axis and Y-axis; the memory pixel allotment numbers of 256:212; and the application of the same 5 V to the resistance surface RX for X-axis detection and to the resistance surface RY for Y-axis detection. Also, data conversion then takes place using the A/D converter 8 which has a resolution of 256. At this time, with regard to the detection of the X-axis coordinate, the A/D converter 8, having a resolution of 256, is used for converting the voltage for the X-axis input position. This is then stored in the image memory section 9, which is a 256 pixel memory.
However, with Y-axis coordinate detection, the voltage corresponding to the Y-axis input position uses the A/D converter 8 which has a resolution of 256. This then has to be made into 212 step data to correspond with the number of memory pixels. This is, of course, extremely difficult and the image memory 9 is therefore unsuitable for processing the Y-coordinate data.
As a result, an external resistor Rg is connected in series via the electrode 1b so as to follow the direction of, for example, the Y-axis (i.e. the short axis). The value of the external resistor Rg is then chosen so that the ratio between the voltage dropped across the resistor RY for the Y-axis input coordinate surface and the voltage dropped across the external resistor Rg is the same as the ratio between the length of the Y-axis and the length of the X-axis minus the Y-axis. For example, in the example where X: Y=256:212, the ratio RY:Rg is taken to be 212:44. As the voltage detected on the resistor RY is adjusted for a resolution of 256 in this way, the aforementioned problem no longer exists.
The external resistor Rg can also be set up in the same way as in the case of the example shown in FIG. 4 and deficiencies in the X-Y pixel ratio can be adjusted.
However, with normal flat board resistors for detecting positions on coordinate axes, the precision of the resistor RX for the X-axis surface and the resistor RY for the Y-axis surface is not very high.
If the resistance surface is formed by printing, on the whole, the resistance of the resistance surface area is fairly uniform. However, the overall resistance of each manufactured input detection member varies by, for example, plus or minus twenty percent.
It is therefore necessary for the external resistor Rg to be a variable resistor. In order to resolve deficiencies in the X-Y pixel ratio, it is then necessary to adjust the resistance of the external resistor Rg for each coordinate input apparatus at the time of manufacture so that the ratio RY:Rg becomes the value mentioned above, or a number of times that value.
The inclusion of an external resistor Rg in the conventional coordinate input apparatus means that the number of parts is increased along with cost. Also, the amount of work involved in adjusting the resistance of the resistor Rg makes the process inefficient.